Some conventional monorail conveyor structures have a wheeled unit that is detachably supported on the main body of the carriage. In these the main body of the carriage has a vertical support column located at one side of the guide rail, and upper and lower projected parts are provided integrally to extend from the upper and lower ends of the vertical support column to the upper and lower sides of the guide rail.
In that type of conveyor the upper extending part of the main body of the carriage usually has two front and rear arms independently of one another at the front and rear of the drive wheel and follower wheel of the conveying tramcar, and steering rollers with vertical axes are provided on the top and the bottom of these arms to contact the sides of the guide rail.
When a conveying tramcar of this kind carries large and heavy articles, the large load acts on the carriage and torsionally deforms the arms in the upper extending part of the main body of the carriage so that normal contact between the roller with the vertical aids and the guide rail is no longer possible, obstructing a smooth travel of the carriages, and damaging the arms or the rollers, or both.
In the known monorail tramcar type conveyors art the reduction gear of the drive wheel unit in the driven carriage, has the drive wheel attached to its output shaft. A motor is provided on the upper end of the main body of the driven carriage while the freely rolling carriage contains the follower wheel unit supporting the follower wheel from the upper end of the main body. Since the follower wheel unit that supports the follower wheel is smaller and lower than the reduction gear, a lower supporting unit is provided in this kind of conventional conveyor, for supporting the surface for holding the article to be conveyed from the side of the drive wheel unit (reduction gear), and provides a higher support unit for the surface that holds the article to be conveyed from the side of the follower wheel unit. The surface that holds the article to be conveyed, can be supported by the upper end of the drive wheel unit (reduction gear) and the upper end of the follower wheel unit, whereby front and rear surface supporting units are provided that hold the surface that holds the article to be conveyed. These that are different in tructure and size from each other.
According to such conventional construction, since the two supporting units that have to be provided for supporting the surface that holds the article to be conveyed, are different in structure and size from each other, this results not only in increased costs, but construction requires two different supporting units to be provided in the respective positions.
The conveying tramcar of the prior art requires a control unit to electrically actuate the motor for the driven carriage and to provide a control signal, both from feed lines supplied through a pantograph collector located on the side of the conveying tramcar. Since the control unit is large and heavy in the known conveying tramcars, the control unit is mounted on the bottom of the surface that holds the article to be conveyed, which in turn is supported by the driven carriage and the freely rolling carriage.
Since the driven carriage and the freely rolling carriage are supported rotatably around vertical shafts relative to the surface that holds the article to be conveyed, so that the tramcar can travel smoothly on straight and curved routes, connecting cables between the motor of the driven carriage and the control unit at the side of the surface that holds the article to be conveyed and between the pantograph collector mounted from the driven carriage or the freely rolling carriage and the control unit, have to be so that they do not hinder a horizontal swinging motion which takes place between the carriages and the surface that holds the article to be conveyed. This increases the wiring costs, and the service life of the cables is short.
In this kind of conveyor, if the article to be conveyed which is placed on the base of supporting the same is longer than the distance between the powered carriage and the freely rolling carriage, an auxiliary carriage is connected through a connecting rod at least to either or both of the carriages to prevent the articles to be conveyed from colliding with each other when the tramcars are close to each other. That auxiliary carriage is equipped with a detector for detecting a stopped tramcar, thereby automatically to stop the next tramcar to avoid collision.
In the conventional tramcar equipped with the auxiliary carriage, that carriage stands in a stable manner, by itself, on the guide rail. More specifically, since the roller with vertical axes is held on the guide rail, it does not prevent the auxiliary carriage from falling down across the guide rail when only one wheel is in contact with the upper surface of the guide rail. Thus, it also cannot hold the auxiliary carriage by itself in a stable manner to prevent the same from falling down in the traveling direction. Therefore, two wheels have to be proyided in the longitudinal direction, or a back-up roller should be placed in juxtapositic guide rail, so that the roller contacts the bottom surface of the guide rail. This is a serious drawback, because it requires a large structure and it is costly.